1. Field of the Invention
The present invention relates generally to an external electric power generation system for supplying power to an aircraft being serviced on the ground, and more particularly to a ground-based aircraft electric power generation system having a voltage regulator that selects from multiple points of regulation.
2. Description of the Related Art
Electrical power generation systems are often located externally on ground power carts at airports for providing electrical power to aircraft. More specifically, an electrical power generation system, sometimes contained in a wheeled ground power cart, supplies electrical power to an aircraft while the aircraft is being serviced on the ground. Electrical power is supplied from a power source located on the ground power cart to the aircraft via a cable that may range in length from 40 feet to 80 feet or even greater. To provide electrical power to the aircraft, a worker connects the end of the cable to a receptacle on the aircraft and operates a power switch, located on the ground power cart, to apply voltage to the cable. In order to save time, the worker sometimes may turn on the power switch before connecting the cable to the receptacle on the aircraft. While procedures may be in place to prevent this scenario, this presents the risk that a spark may be created during connection of the cable to the aircraft, which may ignite flammable fumes and cause a fire. To avoid such accidents, the electrical power generation system may include a contactor, which isolates the power source from the cable until the cable is connected to the aircraft and the contactor is activated.
In addition to providing electrical power, multi-function ground power carts can provide additional features to assist the servicing of the aircraft on the ground. These features may include a hydraulic power system, a conditioned air-cooling system, a liquid cooling system, a nitrogen recharging system, and a compressed air system. These additional systems may require electrical power, which can be provided by the electrical power generation system. These additional systems represent additional loads on the electrical power generation system.
The electrical power generation system is powered by a prime mover, for example, a gas turbine engine or a diesel engine, located on the ground power cart. The output shaft of the prime mover is coupled to a three-phase alternating current generator, which converts the rotational output of the prime mover into electrical power having a voltage and a current. These types of generators could be used, depending on the aircraft to be serviced.
The electrical power generation system also can include a voltage regulator with a single input that senses voltage and regulates the voltage at a single point of regulation, e.g., at the output of the generator or at the end of the cable near the aircraft. One reason to regulate the voltage is to ensure that the aircraft is receiving the correct amount of electrical power. One drawback of regulating the voltage at the output point of the generator is that voltage drops may occur across the power cable resulting in a lower voltage than needed at the aircraft. One drawback of regulating the voltage at the end of the cable is that when the contactor is open (de-energized), electric energy is prevented from traveling along the cable, i.e., between the power source and the aircraft, and therefore there is no voltage to regulate. That is, when the contactor is open, such a voltage regulator is unable to properly regulate the voltage, for the additional loads, that may be supplied by the output of the generator. Hence, in certain situations, the voltage may not be properly regulated when the contactor is open, and can only be regulated when the contactor is closed (energized).
Thus, it should be appreciated that there is a need for an external ground-based electrical power generation system that overcomes the drawbacks of the above conventional voltage regulator schemes in a multi-function ground power cart. The present invention fulfills this need as well as others.